1. Field Of The Invention
The invention relates to a process for preparing .gamma.-mercaptocarboxylic acid derivatives from .gamma.-lactones and also new .beta.-substituted .gamma.-thiolactones as intermediates.
2. Background Art
.gamma.-Mercaptocarboxylic acids and their derivatives such as esters and amides are intermediates, for example, in the synthesis of leucotriene antagonists (European Published Patent Application No. 0480717). The known processes for preparing .gamma.-mercaptocarboxylic acid derivatives start, for example, with the corresponding .gamma.-halocarboxylic acid derivatives whose halogen atoms are replaced, by means of nucleophilic substitution using inorganic sulfides or hydrogen sulfides, by the thiol group. It is also possible to use, in place of the halogen compounds, sulfonic acid esters of the corresponding hydroxycarboxylic acid, for example, the mesylates or tosylates, which can also be reacted with organic sulfur compounds, such as, thiocarboxylic acids or their salts, to give the mercapto compounds. All of these processes have the disadvantage that they first require the introduction of an "assistant substituent" (halide, sulfonate) which is subsequently cleaved off again and finally has to be disposed of as waste.